1. Field of the Invention
The present invention relates to compositions for treating subterranean zones penetrated by well bores. The compositions include polymer complexes and aqueous treating fluids comprised of water and a water soluble fluid loss additive comprised of a polymer complex.
2. Description of the Prior Art
Well treating fluids are used in a variety of operations and treatments in oil and gas wells. Such operations and treatments include well completion operations such as gravel packing to prevent formation solids from being carried out of the well bore with produced hydrocarbon fluids. In gravel packing, suspended gravel particles are carried into a subterranean zone containing a screen in which a gravel pack is to be placed by a viscous gelled treating fluid. Once the gravel pack is placed in the zone, the viscous gelled fluid is broken (the viscosity is reduced) and recovered (returned to the surface). In order to prevent the loss of fluid components of the treating fluid into permeable formations penetrated by the well bore, a fluid loss control additive is included in the treating fluid. The gravel pack formed in the well bore functions as a filter to separate formation solids from produced fluids while permitting the produced fluids to flow into and through the well bore.
Aqueous well treating fluids containing hydraulic cement are utilized extensively in the construction and repair of oil and gas wells. For example, hydraulic cement compositions are used in primary well cementing operations which involve the placement of a cement composition into the annular space between the walls of a well bore and the exterior surfaces of a pipe string such as casing disposed therein. The cement composition is permitted to set in the annular space thereby forming an annular sheath of hardened impermeable cement therein. The objective of the cement sheath is to physically support and position the pipe string in the well bore and bond the pipe string to the walls of the well bore whereby the undesirable migration of formation fluids between subterranean zones penetrated by the well bore is prevented.
An example of a production stimulation treatment utilizing a well treating fluid is hydraulic fracturing. That is, a viscous gelled aqueous treating fluid, referred to in the art as a fracturing fluid, is pumped through the well bore into a subterranean zone to be stimulated at a rate and pressure such that fractures are formed and extended into the subterranean zone. The fracturing fluid also carries particulate proppant material, e.g., sand, into the fractures. The proppant material is suspended in the viscous fracturing fluid so that the proppant material is deposited in the fractures when the viscous fracturing fluid is broken and recovered. The proppant material functions to prevent the formed fractures from closing whereby conductive channels are formed through which production fluids can flow to the well bore. In order to prevent the loss of the fracturing fluid to permeable subterranean formations, a water soluble fluid loss control additive is included in the fracturing fluid. After the viscous fracturing fluid has been pumped into a subterranean zone in a formation and fracturing of the zone has taken place, the fracturing fluid is removed from the formation to allow produced hydrocarbons to flow through the created fractures. Generally, the removal of the viscous fracturing fluid is accomplished by converting the fracturing fluid into a low viscosity fluid. This is accomplished by adding a delayed breaker, i.e., a viscosity reducing additive, to the fracturing fluid prior to pumping it into the subterranean zone to be fractured.
The success of gravel packing operations, primary cementing operations, fracturing operations and other operations utilizing aqueous well treating fluids depends, at least in part, on the ability of the treating fluid used to retain water until it has been placed in a desired well location. That is, as an aqueous treating fluid is pumped through the well bore and contacts permeable subterranean formations penetrated thereby, water included in the treating fluid can be lost to the permeable formations. The loss of water from the treating fluid can prevent the treating fluid from functioning in the manner intended. For example, when portions of the water forming a cement composition are lost, the consistency of the cement composition is also lost which can prevent the composition from being placed in the intended location, the composition can become too viscous for placement and/or the composition fractures subterranean formations whereby all or part of the composition is lost. While lightweight foamed aqueous treating fluids such as foamed cement compositions are often utilized, such foamed treating fluids are also subject to fluid loss when in contact with permeable surfaces.
Heretofore, a variety of fluid loss reducing additives have been developed and used in aqueous well treating fluids. Such additives reduce the loss of liquids, usually water, from such treating fluids when the treating fluids are in contact with permeable surfaces. While the heretofore utilized fluid loss control additives have achieved varying degrees of success, there is a continuing need for improved fluid loss control additives which can be utilized in non-foamed and foamed aqueous well treating fluids and which effectively reduce fluid loss from the aqueous well treating fluids at high temperatures.